Since the wave gear drive was invented by C. W. Musser (see U.S. Pat. No. 2,906,143), various types of wave gear drive have been invented by many researchers, including Musser and the present inventor. There have also been various inventions relating to the tooth profile of the gears used in wave gear drives. The present inventor has proposed making the basic tooth profile an involute tooth profile (see JP-B 45-41171), and a method of designing a tooth profile in which the addendum profiles for wide contact between the rigid internal gear and flexible external gear are derived using a rack approximation of the meshing between the two gears (see JP-A 63-115943 and JP-A 64-79448). There has also been proposed an invention for avoiding interference between rack-approximated tooth profiles (see JP-A 7-167228).
There is a strong market demand for wave gear drives with improved performance, especially improved load capability. The main elements that govern the load capability of a wave gear drive are the fatigue strength of the tooth bottom rim of the flexible external gear and the fatigue strength of the inner rolling contact surface of the wave generator, particularly at locations in the vicinity of the major axis of the elliptically deformed flexible external gear.
An object of the present invention is to provide a wave gear drive having a tooth profile that is able to reduce the stresses generated at the above two locations.